For three years I used pre and post-tests as assessment tools for measuring the preparedness and performance of my EFL students. In addition to measuring how much students have improved in one semester of study, the pre/post-test can be a valuable diagnostic tool for more effective teaching.
After the pre-test identifies the weak students in a class, it is the teacher's responsibility to give extra remedial instruction. For example, if a student is not reading at the fifth-grade level as measured by a post-test given at the end of fourth grade, the teacher should find instructional materials at a lower grade level. A dedicated teacher would then find time during his lunch hour or breaks during the day to give extra individual help to the student. The teacher would also encourage the student's parents to assist with remedial tutor ing.
Pre/post-test functions as a teacher diagnostic tool in the following five ways:
I had just finished giving pre-tests to EFL students who were taking my reading and writing course. More than 70 percent of the students scored less than 50 on the mechanics of writing. This included capitalization, spelling, punctuation, verb tense usage, and other grammatical errors. This identified a topic which the students still didn't know.
You are correct in stating that the teacher will not share (or show) the pre-test mistakes to the student, because the student will then know what to expect for the post-test.
A much higher post-test score should indicate that a student has learned certain topics in comparing pre-test and post-test scores. If the scores are about the same, or if the post-test score is lower than the pre-test score, in all indications this measures that topics were not learned in the course.
If 75 - 80 percent of the students score above 80 on a certain topic, this would indicate that most of the students already know the subject matter. I once had a class in which 60 percent of the students scored more than 75 on the pre-test.